1. Technical Field
The present invention relates to real-time virtual endoscopy and, more particularly, to methods and systems for real-time 3-D visualization and navigation for interventional procedures.
2. Description of the Related Art
Medical imaging is generally recognized as important for diagnosis and patient care with the goal of improving treatment outcomes. In recent years, medical imaging has experienced an explosive growth due to advances in imaging modalities such as x-rays, computed tomography (CT), magnetic resonance (MR) imaging and ultrasound. These modalities provide noninvasive methods to study internal organs in vivo, producing anatomical and functional image data in 2-D, 3-D or even 4-D (3-D+time). The image data is typically analyzed by a radiologist, who bases his diagnosis on findings in single image slices or in some other graphical representation, e.g., volume rendering.
Advances in magnetic resonance (MR) technology and methodology have triggered research studies in the field of interventional MRI (iMRI). Jolesz provides a general overview of the field of iMRI. Jolesz, F. A., “Interventional and intraoperative MRI: a general overview of the field,” In Journal of Magnetic Resonance Imaging, January-February 1998, 8(1):3-7. Tsekos provides approaches towards performing real-time coronary MR angiography (MRA) and MR-guided coronary interventions. Tsekos, N. V., Atalar, E., Li, D., Omary, R. A., Serfaty, J. M., Woodard, P. K., “Magnetic Resonance Imaging-Guided Coronary Interventions,” In Journal of Magnetic Resonance Imaging, 2004, 19(6):734-49. Besides avoiding ionizing radiation exposure of the patient and the physician performing the procedures, performing diagnostic and therapeutic procedures under MRI guidance offers advantages over the current standard of X-ray guidance. For example, high-spatial-resolution MR images, excellent soft-tissue contrast, and selection of arbitrary scan planes in 3-D volumes, without the need to manually reposition the patient or the imaging device, are features that have drawn attention to iMRI.
While not yet applied in the clinical realm, iMRI is an area of intense research. Significant advances have been made in the development of specialized pulse sequences and catheter design and tracking methods. Boll compares pulse sequences for interventional device guidance during magnetic resonance (MR) imaging to evaluate the dependence of sequence selection on the anatomic region of the procedure. Boll, D. T., Lewin, J. S., Duerk, J. L., Aschoff, A. J., Merkle, E. M., “Comparison of MR imaging sequences for liver and head and neck interventions: is there a single optimal sequence for all purposes?” In Academic Radiology, May 2004, 11(5):506-15. Buecker provides simultaneous MR real-time active tip tracking and near real-time depiction of the vascular anatomy for percutaneous angioplasty (PTA) of iliac arteries under MR guidance. Buecker, A., Adam, G. B., Neuerburg, J. M., Kinzel, S., Glowinski, A. Schaeffter, T., Rasche, V., van Vaals, J. J. Guenther, R. W., “Simultaneous real-time visualization of the catheter tip and vascular anatomy for MR-guided PTA of iliac arteries in an animal model,” In Journal of Magnetic Resonance Imaging, August 2002, 16(2): 201-8. Another element of iMRI under development is the visualization and navigation interface. It is desirable to minimize the resources needed for scanner interaction while at the same time providing the most meaningful presentation of the acquired data to is the physician in real-time.
Different approaches to MR image visualization for interventional procedures have been proposed. Current techniques include 2-D image display of single or multiple slices in real-time, 2-D projections of MR angiography data and 3-D volume rendering. Zhang provides a target-navigation technique in which the MR scan plane was defined automatically by the invasive device orientation and target tissue location. Zhang, Q., Wendt, M. Aschoff, A., Zheng, L., Lewin, J. Duerk, J., “Active MR guidance of interventional devices with target-navigation,” In Magnetic Resonance in Medical Sciences, July 2000, 44(1):56-65. Serfaty provides a 2-D projection technique with no section selection. Serfaty, J. M., Atalar, E., Declerck, J., Karmakar, P. Quick, H. H., Shunk, K. A., Heldman, A. W., Yang, X: “Real-Time projection MR angiography: feasibility study,” In Radiology, October 2000, 217(1):290-5. Guttman provides a system for real-time volume renderings from 2-D multi-slice or 3-D MR pulse sequences. Guttman, M. A., Lederman, R. J., Sorger, J. M., McVeigh, E. R., “Real-time volume rendered MRI for interventional guidance,” In Journal of Cardiovascular Magnetic Resonance, 2002, 4(4): 431-42.
While virtual endoscopy is generally accepted as a standard diagnostic tool for performing offline procedures, a real-time 3-D first-person view could help a physician to perform interventional procedures. For example, such a view could help monitor stent placement for abdominal aortic aneurysms and to assess and prevent possible tearing of the adjacent wall. Visualizing a catheter tip in a real-time 3-D view could help a physician to guide the device to the target tissue for a trial ablation.
Conventional MR scanning systems are designed to generate diagnostic images using a previously defined set of imaging parameters. Various real-time scanner control systems have been built for different applications. These systems are generally limited to scan plane control and direct parameter manipulation.